1. Field of the Invention
The present invention relates to an electro-optical device, typically an EL (electroluminescence) display device formed by a semiconductor element (an element using a semiconductor thin film) made on a substrate, and to electronic equipment (an electronic device) having the electro-optical device as a display (also referred to as a display portion). In particular, the present invention relates to a manufacturing method thereof.
2. Description of the Related Art
Techniques of forming a TFT on a substrate have been widely progressing in recent years, and developments of applications to an active matrix type display device are advancing. In particular, a TFT using a polysilicon film has a higher electric field effect mobility (also referred to as mobility) than a TFT using a conventional amorous silicon film, and high speed operation is therefore possible. As a result, it becomes possible to perform pixel control, conventionally performed by a driver circuit external to the substrate, by a driver circuit formed on the same substrate as the pixel.
This type of active matrix display device has been in the spotlight because of the many advantage which can be obtained by incorporating various circuits and elements on the same substrate in this type of active matrix display device, such as reduced manufacturing cost, small size, increased yield, and higher throughput.
Switching elements are formed by a TFT for each of the pixels in the active matrix display device, current control is performed by driver elements using the switching elements, and an EL layer (electroluminescence layer) is made to emit light. A typical pixel structure at this time is disclosed in, for example, U.S. Pat. No. 5,684,365 (Japanese Patent Application Laid-open No. 8-234683) and Japanese Patent Application Laid-open No. Hei 10-189252.
In performing color display of these EL display devices, trials for disposing EL layers that emit three primary colors of red (R), green (G) and blue (B) on respective pixels have been made. However, most of the materials used in general as EL layers, are organic materials and the patterning is extremely difficult. This is because EL materials themselves are very weak to moisture, and it is difficult to treat them as they easily dissolve even in a developing solution.
As a technology for solving such a problem, a technique of forming EL layers by ink jet method is suggested. For example, an active matrix EL display in which EL layers are formed ink jet method is disclosed in Japanese Patent Application Laid-Open No. Hei 10-012377. Further, similar technique is also disclosed in Shimada, T. et al., SID 99 DIGEST, P376–9, “Multicolor Pixel Patterning of Light-Emitting Polymers by Ink-jet Printing.”
However, because ink jet method is performed under normal pressure, it is disadvantageous in the point that contaminants in the external atmosphere are easily taken. Namely, it has a problem that because EL layers are formed in a state of easily including mobile ions such as alkaline metals, diffusion of the alkaline metals therefore can give fatal damage to the TFTs. Note that throughout the Specification alkaline metals and alkali-earth metals are together referred to as “alkaline metals”.